1.Field of the Invention
The invention relates to mixers and emulsifiers used in industrial applications. More particularly, the invention relates to rotors and stators which are used in industrial mixers and emulsifiers.
2.State of the Art
Industrial mixers and emulsifiers are used to blend various materials such as adhesives, coatings, cosmetics, foods, pharmaceuticals, plastics, etc. Depending on the processing requirements, mixers/emulsifiers may be arranged as a "batch" mixer or an "in-line" mixer. In either case, high speed mechanical and hydraulic shearing forces are created by rotating a rotor relative to a stator such that material is drawn axially into the rotor-stator assembly and dispersed radially outward from the rotor-stator assembly. Prior art FIG. 1 shows a schematic representation of a typical rotor-stator assembly 10. The rotor 12 is a stainless steel disk 14 with a number of teeth or vanes 16 and the stator 18 is a stainless steel cylinder having radial openings 20. The rotor 12 is mounted coaxially within the stator 18 and is rotated at a typical speed of 3600 rpm. A close clearance between the rotor and the stator generates a shearing action. Many different rotor and stator designs are in use today. Prior art FIG. 2 shows another type of rotor-stator assembly 22 shown in schematic form. Here the rotor 24 and the stator 26 are substantially similar stainless steel cylinders each having a plurality of teeth or blades 28, 30 which define a plurality of radial openings 32, 34 in the cylinder. The rotor 24 has a slightly smaller diameter than the stator 26 and generates a shearing action between the openings 32, 34 as it rotates relative to the stator 26. Prior art FIG. 3 shows a "multi-rowed" rotor-stator assembly 36. The multi-rowed rotor 38 and the multi-rowed stator 40 are similar cylindrical members each having arrays of teeth 42, 44 arranged in concentric circles. The rotor 38 and the stator 40 are dimensioned so that the rotor 38 fits inside the stator 40 with the rotor teeth 42 and the stator teeth 44 interleaved. Rotor-stator assemblies are available in a variety of sizes, ranging in diameter from two to thirteen inches. The teeth or vanes on a rotor-stator typically have a height which is approximately one tenth to one fifth the diameter of the rotor-stator.
Co-owned U.S. Pat. No. 5,632,596 discloses a rotor-stator assembly having vanes with slots as shown in prior art FIGS. 4-8. The stator 100 is a stainless steel disk having a central fluid opening 102 and a pair of diametrically opposed mounting holes 104, 106. One surface of the stator 100 is provided with seven concentric vanes 108, 110, 112, 114, 116, 118, 120 which define six concentric wells 109, 111, 113, 115, 117, 119. Forty-four radial slots, e.g. 122, are arranged at intervals of 8.degree., thereby defining forty-four teeth, e.g. 124, in each vane. The rotor 150 is a stainless steel disk having a central keyed mounting hole 152. One surface of the rotor 150 is provided with seven concentric vanes 158, 160, 162, 164, 166, 168, 170 which define six concentric wells 159, 161, 163, 165, 167, 169. Forty-four radial slots, e.g. 172, are arranged at intervals of 8.degree., thereby defining forty-four teeth, e.g. 174, in each vane. The rotor 150 is dimensioned to match the stator 100. The vanes in the rotor are placed so that they fit into the wells in the stator. The overall heights of the rotor 150 and the stator 100 are dimensioned to provide proper clearance between the rotor and the stator as shown in FIG. 8.
The rotor-stator of the '596 patent achieved a higher amount of shear than the prior art rotor-stators which preceded it. However, there is a limit to the amount of shear which can be achieved with this design. In particular, it has been discovered that the slots in the vanes can allow some material to pass through without being sheared very much.